Gate structures in semiconductor devices

ABSTRACT

A semiconductor device with different configurations of gate structures and a method of fabricating the same are disclosed. The method includes forming a fin structure on a substrate, forming a gate opening on the fin structure, forming an interfacial oxide layer on the fin structure, forming a first dielectric layer over the interfacial oxide layer, forming a dipole layer between the interfacial oxide layer and the first dielectric layer, forming a second dielectric layer on the first dielectric layer, forming a work function metal (WFM) layer on the second dielectric layer, and forming a gate metal fill layer on the WFM layer. The dipole layer includes ions of first and second metals that are different from each other. The first and second metals have electronegativity values greater than an electronegativity value of a metal or a semiconductor of the first dielectric layer.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs, fin field effect transistors(finFETs), and gate-all-around (GAA) FETs. Such scaling down hasincreased the complexity of semiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures.

FIG. 1A illustrates an isometric view of a semiconductor device, inaccordance with some embodiments.

FIGS. 1B-1E illustrate cross-sectional views of a semiconductor devicewith different gate structures, in accordance with some embodiments.

FIG. 1F illustrates device characteristics of a semiconductor devicewith different gate structures, in accordance with some embodiments.

FIG. 2 is a flow diagram of a method for fabricating a semiconductordevice with different gate structures, in accordance with someembodiments.

FIGS. 3A-15B illustrate cross-sectional views of a semiconductor devicewith different gate structures at various stages of its fabricationprocess, in accordance with some embodiments.

FIG. 16 is a flow diagram of a method for fabricating a semiconductordevice with different gate structures, in accordance with someembodiments.

FIGS. 17A-26B illustrate cross-sectional views of a semiconductor devicewith different gate structures at various stages of its fabricationprocess, in accordance with some embodiments.

FIGS. 27-28 illustrates device characteristics of a semiconductor devicewith different gate structures at various stages of its fabricationprocess, in accordance with some embodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the processfor forming a first feature over a second feature in the descriptionthat follows may include embodiments in which the first and secondfeatures are formed in direct contact, and may also include embodimentsin which additional features may be formed between the first and secondfeatures, such that the first and second features may not be in directcontact. As used herein, the formation of a first feature on a secondfeature means the first feature is formed in direct contact with thesecond feature. In addition, the present disclosure may repeat referencenumerals and/or letters in the various examples. This repetition doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

In some embodiments, the terms “about” and “substantially” can indicatea value of a given quantity that varies within 5% of the value (e.g.,±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely examplesand are not intended to be limiting. The terms “about” and“substantially” can refer to a percentage of the values as interpretedby those skilled in relevant art(s) in light of the teachings herein.

The fin structures disclosed herein may be patterned by any suitablemethod. For example, the fin structures may be patterned using one ormore photolithography processes, including double-patterning ormulti-patterning processes. Double-patterning or multi-patterningprocesses can combine photolithography and self-aligned processes,allowing patterns to be created that have, for example, pitches smallerthan what is otherwise obtainable using a single, directphotolithography process. For example, a sacrificial layer is formedover a substrate and patterned using a photolithography process. Spacersare formed alongside the patterned sacrificial layer using aself-aligned process. The sacrificial layer is then removed, and theremaining spacers may then be used to pattern the fin structures.

The required gate voltage—the threshold voltage (Vt)—to turn on a fieldeffect transistor (FET) can depend on the semiconductor material of theFET channel region and/or the effective work function (EWF) value of agate structure of the FET. For example, for an n-type FET (NFET),reducing the difference between the EWF value(s) of the NFET gatestructure and the conduction band energy of the material (e.g., 4.1 eVfor Si or 3.8 eV for SiGe) of the NFET channel region can reduce theNFET threshold voltage. For a p-type FET (PFET), reducing the differencebetween the EWF value(s) of the PFET gate structure and the valence bandenergy of the material (e.g., 5.2 eV for Si or 4.8 eV for SiGe) of thePFET channel region can reduce the PFET threshold voltage. The EWFvalues of the FET gate structures can depend on the thickness and/ormaterial composition of each of the layers of the FET gate structure. Assuch, FETs can be manufactured with different threshold voltages byadjusting the thickness and/or material composition of the FET gatestructures.

Due to the increasing demand for multi-functional low power portabledevices, there is an increasing demand for FETs with lower and/ordifferent threshold voltages, such as threshold voltages lower than 100mV. One way to achieve multi-Vt devices with low threshold voltages inFETs can be with different work function metal (WFM) layer thicknessesgreater than about 4 nm (e.g., about 5 nm to about 10 nm) in the gatestructures. However, the different WFM layer thicknesses can beconstrained by the FET gate structure geometries. Also, depositingdifferent WFM layer thicknesses can become increasingly challenging withthe continuous scaling down of FETs (e.g., GAA FETs, finFETs, and/orMOSFETs).

The present disclosure provides example multi-Vt devices with FETs(e.g., finFETs) having ultra-low threshold voltages (e.g., about 20 mVto about 100 mV) different from each other and provides example methodsof forming such FETs on the same substrate. The example methods formNFETs and PFETs with WFM layer of similar thicknesses, but withultra-low and/or different threshold voltages, on the same substrate.These example methods can be more cost-effective (e.g., cost reduced byabout 20% to about 30%) and time-efficient (e.g., time reduced by about15% to about 20%) in manufacturing reliable FET gate structures withlower and/or different threshold voltages than other methods of formingFETs with similar dimensions and threshold voltages on the samesubstrate. In addition, these example methods can form FET gatestructures with much smaller dimensions (e.g., thinner gate stacks) thanother methods of forming FETs with similar threshold voltages.

In some embodiments, NFETs and PFETs with different gate structureconfigurations, but with similar WFM layer thicknesses, can beselectively formed on the same substrate to achieve ultra-low and/ordifferent threshold voltages. The different gate structures can havehigh-K (HK) gate dielectric layers doped with different metallicdopants. The different metal dopants can induce dipoles of differentpolarities and/or concentrations at interfaces between the HK gatedielectric layers and interfacial oxide (TO) layers. The dipoles ofdifferent polarities and/or concentrations result in gate structureswith different EWF values and threshold voltages. In some embodiments,HK gate dielectric layers can be doped with dopants of two differentmaterials to induce dipoles of different materials that provide strongerelectric fields and lower threshold voltages. Thus, controlling thedopant materials and/or concentrations in the HK gate dielectric layerscan tune the EWF values of the NFET and PFET gate structures, and as aresult can adjust the threshold voltages of the NFETs and PFETs withoutvarying the WFM layer thicknesses. In some embodiments, instead of thedoped HK gate dielectric layer, PFET gate structure can include dualmetal oxide layers interposed between the HK gate dielectric and the IOlayer to induce dipoles of different materials between the HK gatedielectric layer and the IO layer.

FIG. 1A illustrates an isometric view of a semiconductor device 100 withPFET 102P and NFET 102N, according to some embodiments. PFET 102P andNFET 102N can have different cross-sectional views, as illustrated inFIGS. 1B-1E, according to various embodiments. FIGS. 1B-1E illustratecross-sectional views of PFET 102P and NFET 102N along respective linesA-A and B-B of FIG. 1A. FIGS. 1B-1E illustrate cross-sectional views ofsemiconductor device 100 with additional structures that are not shownin FIG. 1A for simplicity. The discussion of elements of PFET 102P andNFET 102N with the same annotations applies to each other, unlessmentioned otherwise.

Referring to FIG. 1A, NFET 102N can include an array of gate structures112N disposed on fin structure 106N, and PFET 102P can include an arrayof gate structures 112P disposed on fin structure 106P. NFET 102N canfurther include an array of S/D regions 110N disposed on portions of finstructure 106N that are not covered by gate structures 112N. Similarly,PFET 102P can further include an array of epitaxial S/D regions 110Pdisposed on portions of fin structure 106P that are not covered by gatestructures 112P.

Semiconductor device 100 can further include gate spacers 114, shallowtrench isolation (STI) regions 116, etch stop layers (ESLs) 117, andinterlayer dielectric (ILD) layers 118. In some embodiments, gatespacers 114, STI regions 116, ESLs 117, and ILD layers 118 can includean insulating material, such as silicon oxide, silicon nitride (SiN),silicon carbon nitride (SiCN), silicon oxycarbon nitride (SiOCN), andsilicon germanium oxide. In some embodiments, gate spacers 114 can havea thickness of about 2 nm to about 9 nm for adequate electricalisolation of gate structures 112N and 112P from adjacent structures.

Semiconductor device 100 can be formed on a substrate 104 with PFET 102Pand NFET 102N formed on different regions of substrate 104. There may beother FETs and/or structures (e.g., isolation structures) formed betweenPFET 102P and NFET 102N on substrate 104. Substrate 104 can be asemiconductor material, such as silicon, germanium (Ge), silicongermanium (SiGe), a silicon-on-insulator (SOI) structure, and acombination thereof. Further, substrate 104 can be doped with p-typedopants (e.g., boron, indium, aluminum, or gallium) or n-type dopants(e.g., phosphorus or arsenic). In some embodiments, fin structures106P-106N can include a material similar to substrate 104 and extendalong an X-axis.

Referring to FIGS. 1B-1C, PFET-NFET 102P-102N can include S/D regions110P-110N and gate structures 112P-112N. For PFET 102P, S/D regions 110Pcan include an epitaxially-grown semiconductor material, such as Si andSiGe, and p-type dopants, such as boron and other suitable p-typedopants. For NFET 102N, S/D regions 110N can include anepitaxially-grown semiconductor material, such as Si, and n-typedopants, such as phosphorus and other suitable n-type dopants.

Gate structures 112P-112N can be multi-layered structures. Gatestructures 112P-112N can include (i) gate oxide structures 122P-122Ndisposed on respective fin structures 106P-106N, (ii) work functionmetal (WFM) layers 124P-124N disposed on respective gate oxidestructures 122P-122N, and (iii) gate metal fill layers 126P-126Ndisposed on respective WFM layers 124P-124N.

Referring to FIG. 1B, in some embodiments, gate oxide structure 122P caninclude (i) an IO layer 128P disposed on fin structure 106P, (ii) afirst metal oxide layer 132P disposed on IO layer 128P, (iii) a secondmetal oxide layer 133P disposed on first metal oxide layer 132P, (iv) adipole layer 130P disposed at an interface between IO layer 128P andfirst metal oxide layer 132P, (v) a first HK gate dielectric layer 134Pdisposed on second metal oxide layer 133P, and (vi) a second HK gatedielectric layer 136P disposed on first HK gate dielectric layer 134P.

IO layer 128P can include an oxide of the material of fin structure106P, such as silicon oxide (SiO₂), silicon germanium oxide (SiGeO_(x)),and germanium oxide (GeO_(x)). The materials of first and second metaloxide layers 132P-133P are different from each other and can induce theformation of two different p-type dipoles in dipole layer 130P. Dipolelayer 130P can include p-type dipoles of (i) first metal ions from firstmetal oxide layer 132P and oxygen ions from IO layer 128P and (ii)second metal ions from second metal oxide layer 133P and oxygen ionsfrom IO layer 128P. The first metal ions are different from the secondmetal ions. First and second metal oxide layers 132P-133P can includeoxides of metals that have electronegativity values greater than theelectronegativity values of metals or semiconductors in first HK gatedielectric layer 134P. In addition, first and second metal oxide layers132P-133P can include oxide materials that have oxygen areal densitiesgreater than the oxygen areal densities of oxide materials in first HKgate dielectric layer 134P. As used herein, the term “oxygen arealdensity” of an oxide material refers to an atomic concentration ofoxygen atoms per unit area of the oxide material.

The larger electronegativity values and oxygen areal densities of firstand second metal oxide layers 132P-133P can induce stronger p-typedipoles in dipole layer 130P compared to dipoles induced at an interfacebetween IO layer 128P and first HK gate dielectric layer 134P in theabsence of first and second metal oxide layers 132P-133P. Also, the twodifferent p-type dipoles can generate a stronger electric field thansingle p-type dipoles and form a more stable dipole layer 130P. Asstronger p-type dipoles can result in lower threshold voltages forPFETs, the use of first and second metal oxide layers 132P-133P can formPFET 102P with a threshold voltage lower than about 100 mV (e.g., about50 mV, about 30 mV, or about 20 mV).

In some embodiments, first and second metal oxide layers 132P-133P caninclude oxides of transition metals, such as zinc oxide (ZnO₂), niobiumoxide (NbO₂), molybdenum oxide (MoO₂), tungsten oxide (WO₃), andtantalum oxide (Ta₂O₅). In some embodiments, first and second metaloxide layers 132P-133P can include oxides of elements from group 13 ofthe periodic table, such as gallium oxide (Ga₂O₃), aluminum oxide(Al₂O₃), and indium oxide (In₂O₃), when first HK gate dielectric layer134P includes HfO₂. In some embodiments, first metal oxide layer 132Pcan include an oxide of a transition metal and second metal oxide layer133P can include an oxide of a material from group 13 of the periodictable. In some embodiments, dipole layer 130P can include Ga—O and Zn—Odipoles when first metal oxide layer 132P includes ZnO and second metaloxide layer 133P includes Ga₂O₃.

In some embodiments, dipole layer 130P can have a higher concentrationof transition metal based dipoles (e.g., Zn—O, Nb—O, Mo—O, W—O, or Ta—O)than group 13 element based dipoles (e.g., Ga—O, Al—O, or In—O) toachieve threshold voltages below about 50 mV (e.g., about 30 mV or 20mV). In such embodiments, first metal oxide layer 132P includes atransition metal oxide with a thickness greater than the thickness ofsecond metal oxide 133P that includes an oxide of group 13 element asthe concentration of dipoles is directly proportional to the thicknessof the dipole source layer. In contrast, to achieve threshold voltagesgreater than 50 mV (e.g. about 70 mV or about 100 mV), dipole layer 130Pcan have a higher concentration of group 13 element based dipoles thantransition metal based dipoles. In such embodiments, first metal oxidelayer 132P includes an oxide of group 13 element with a thicknessgreater than the thickness of second metal oxide 133P that includes atransition metal oxide. In some embodiments, first metal oxide layer132P can include oxides of transition metals and dipole layer 130P caninclude transition metal based dipoles in the absence of second metaloxide layer 133P.

In some embodiments, first and second metal oxide layers 132P-133P canhave thicknesses ranging from about 0.5 nm to about 3 nm. If first andsecond metal oxide layers 132P-133P are thinner than about 0.5 nm, theformation of dipoles in dipole layer 130P may not occur. On the otherhand, if first and second metal oxide layers 132P-133P are thicker than3 nm, diffusion of metal atoms from first and second metal oxide layers132P-133P may degrade first and second HK gate dielectric layers134P-136P, and consequently degrade device performance.

First and second HK gate dielectric layers 134P-136P can include high-kdielectric materials, such as hafnium oxide (HfO₂), titanium oxide(TiO₂), hafnium zirconium oxide (HfZrO), tantalum oxide (Ta₂O₃), hafniumsilicate (HfSiO₄), zirconium oxide (ZrO₂), and zirconium silicate(ZrSiO₂). In some embodiments, first and second HK gate dielectriclayers 134P-136P can include materials similar to or different from eachother. In some embodiments, first and second HK gate dielectric layers134P-136P can have thicknesses similar to or different from each other.In some embodiments, first and second HK gate dielectric layers134P-136P can be undoped.

In some embodiments, p-type WFM (pWFM) layer 124P can includesubstantially Al-free (e.g., with no Al) (i) Ti-based nitrides oralloys, such as TiN, TiSiN, titanium gold (Ti—Au) alloy, titanium copper(Ti—Cu) alloy, titanium chromium (Ti—Cr) alloy, titanium cobalt (Ti—Co)alloy, titanium molybdenum (Ti—Mo) alloy, and titanium nickel (Ti—Ni)alloy; (ii) Ta-based nitrides or alloys, such as TaN, TaSiN, Ta—Aualloy, Ta—Cu alloy, Ta—W alloy, tantalum platinum (Ta—Pt) alloy, Ta—Moalloy, Ta—Ti alloy, and Ta—Ni alloy; or (iii) a combination thereof. Insome embodiments, pWFM layer 124P can include a thickness ranging fromabout 1 nm to about 3 nm. Other suitable dimensions of pWFM layer 124Pare within the scope of the present disclosure. Gate metal fill layer126P can include a suitable conductive material, such as tungsten (W),Ti, silver (Ag), ruthenium (Ru), molybdenum (Mo), copper (Cu), cobalt(Co), Al, iridium (Ir), nickel (Ni), metal alloys, and a combinationthereof.

Referring to FIG. 1C, in some embodiments, gate oxide structure 122N caninclude (i) an IO layer 128N disposed on fin structure 106N, (ii) afirst HK gate dielectric layer 134N disposed on IO layer 128N, (iii) asecond HK gate dielectric layer 136N disposed on first HK gatedielectric layer 134N, and (iv) a dipole layer 130N disposed at aninterface between IO layer 128N and first HK gate dielectric layer 134N.

IO layer 128N can include an oxide of the material of fin structure106N, such as silicon oxide (SiO₂), silicon germanium oxide (SiGeO_(x)),and germanium oxide (GeO_(x)). In some embodiments, first HK gatedielectric layer 134N can include dopants of metals that haveelectronegativity values lower than the electronegativity values ofmetallic or semiconductor materials included in first HK gate dielectriclayer 134N. In some embodiments, first HK gate dielectric layer 134N caninclude dopants of a rare-earth metal, such as Lanthanum (La), Yttrium(Y), Scandium (Sc), Cerium (Ce), Ytterbium (Yb), Erbium (Er), Dysprosium(Dy), and Lutetium (Lu). The metal dopants of first HK gate dielectriclayer 134N can induce the formation of n-type dipoles in dipole layer130N. Dipole layer 130N can include n-type dipoles of metal ions fromthe metal dopants and oxygen ions from IO layer 128N, such as La—Odipoles, when first HK gate dielectric layer 134N includes La dopants.The lower electronegativity value of the metal dopants of first HK gatedielectric layer 134N can induce stronger n-type dipoles in dipole layer130N compared to dipoles induced at an interface between IO layer 128Nand undoped first HK gate dielectric layer 134N. In some embodiments,first and second HK gate dielectric layers 134N-136N can include high-kdielectric materials similar to first and second HK gate dielectriclayers 134P-136P.

In some embodiments, nWFM layer 124N can include titanium aluminum(TiAl), titanium aluminum carbide (TiAlC), tantalum aluminum (TaAl),tantalum aluminum carbide (TaAlC), Al-doped Ti, Al-doped TiN, Al-dopedTa, Al-doped TaN, or a combination thereof. In some embodiments, nWFMlayer 124N can include a thickness ranging from about 1 nm to about 3nm. Other suitable dimensions of nWFM layer 124N are within the scope ofthe present disclosure. Gate metal fill layer 126N can include aconductive material similar to gate metal fill layer 126P.

Referring to FIG. 1D, in some embodiments, gate oxide structure 122Pdoes not include first and second metal oxide layers 132P-133P andincludes first HK gate dielectric layer 135P with dual-metal dopantsinstead of undoped first HK gate dielectric layer 134P (shown in FIG.1B). Instead of first and second metal oxide layers 132P-133P, thedual-metal dopants of first HK gate dielectric layer 135P induces theformation of different p-type dipoles in dipole layer 130P. Dipole layer130P can include p-type dipoles of two different metal ions from thedual-metal dopants of first HK gate dielectric layer 135P and oxygenions from IO layer 128P. First HK gate dielectric layer 135P can includedopants of metals that have electronegativity values greater than theelectronegativity values of metals or semiconductors in first HK gatedielectric layer 135P. In some embodiments, first HK gate dielectriclayer 135P can include dopants of materials from group 13 of theperiodic table, such as Ga, Al, and In, when first HK gate dielectriclayer 135P includes HfO₂. In some embodiments, first HK gate dielectriclayer 135P can include dopants of transition metals, such as Zn, Nb, Mo,W, and Ta. In some embodiments, dipole layer 130P can include Ga—O andZn—O dipoles when first HK gate dielectric layer 135P includes Ga andZn.

In some embodiments, first HK gate dielectric layer 135P can have ahigher concentration of transition metal based dopants (e.g., Zn, Nb,Mo, W, or Ta) than group 13 element based dipoles (e.g., Ga, Al, or In)to achieve threshold voltages below about 50 mV (e.g., about 30 mV or 20mV) as the concentration of dopants is directly proportional to theconcentration of dipoles. In contrast, to achieve threshold voltagesgreater than 50 mV (e.g. about 70 mV or about 100 mV), first HK gatedielectric layer 135P can have a higher concentration of group 13element based dopants than transition metal based dopants. In someembodiments, first HK gate dielectric layer 135P can include transitionmetal based dopants and may not include group 13 element based dopants.

FIG. 1F shows the Hf, Zn, Ga, O₂, and Si concentration profiles 138,139, 140, 142, and 144 across first HK gate dielectric layer 135P and IOlayer 128P along line C-C of FIG. 1D, when first HK gate dielectriclayer 135P includes HfO₂, and Ga and Zn dopants, and IO layer 128Pincludes SiO₂, according to some embodiments. As shown in FIG. 1F, thepeak concentration of Zn dopants (profile 139) is higher than the peakconcentration of Ga dopants (profile 140).

FIG. 2 is a flow diagram of an example method 200 for fabricatingPFET-NFET 102P-102N with cross-sections as shown in FIGS. 1B-1C,according to some embodiments. For illustrative purposes, the operationsillustrated in FIG. 2 will be described with reference to the examplefabrication process for fabricating PFET-NFET 102P-102N as illustratedin FIGS. 3A-15B. FIGS. 3A-15B are cross-sectional views of PFET-NFET102P-102N along lines A-A and B-B of FIG. 1A at various stages offabrication, according to various embodiments. Operations can beperformed in a different order or not performed depending on specificapplications. It should be noted that method 200 may not producecomplete PFET-NFET 102P-102N. Accordingly, it is understood thatadditional processes can be provided before, during, and after method200, and that some other processes may only be briefly described herein.Elements in FIGS. 3A-15B with the same annotations as elements in FIGS.1A-1C are described above.

In operation 205, polysilicon structures and S/D regions are formed onfin structures of a PFET and NFET. For example, as shown in FIGS. 3A-3Bpolysilicon structures 312P-312N and S/D regions 110P-110N are formed onrespective fin structure 106P-106N, which are formed on substrate 104.During subsequent processing, polysilicon structures 312P-312N can bereplaced in a gate replacement process to form gate structures112P-112N. After the formation of S/D regions 110P-110N, ESLs 117A andILD layers 118 can be formed to form the structures of FIGS. 3A-3B.

Referring to FIG. 2 , in operation 210, gate openings are formed on thefin structures. For example, as shown in FIGS. 4A-4B, gate openings412P-412N are formed on respective fin structures 106P-106N. Theformation of gate openings 412P-412N can include etching polysiliconstructures 312P-312N from the structures of FIGS. 3A-3B.

Referring to FIG. 2 , in operations 215-235, gate oxide structures areformed within the gate openings. For example, as described withreference to FIGS. 4A-12B, gate oxide structures 122P-122N (shown inFIGS. 1B-1C) are formed within respective gate openings 412P-412N.

Referring to FIG. 2 , in operation 215, 10 layers are formed within thegate openings. For example, as shown in FIGS. 5A-5B, IO layers 128P-128Nare formed within gate openings 412P-412N. In some embodiments, IOlayers 128P-128N can be formed by exposing the surfaces of finstructures 106P-106N within respective gate openings 412P-412N to anoxidizing ambient. The oxidizing ambient can include a combination ofozone (03), a mixture of ammonia hydroxide, hydrogen peroxide, andwater, and/or a mixture of hydrochloric acid, hydrogen peroxide, water.

The subsequent formation of layers on IO layers 128P-128N in operations220-240 are described with reference to FIGS. 6A-13B, which are enlargedviews of regions 103P-103N shown in respective FIGS. 5A-5B.

Referring to FIG. 2 , in operation 220, first and second metal oxidelayers are selectively formed on the IO layer of the PFET. For example,as described with reference to FIGS. 6A-7B, first and second metal oxidelayers 132P-133P are formed on IO layer 128P. The selective formation offirst and second metal oxide layers 132P-133P can include sequentialoperations of (i) depositing a first metal oxide layer 132 on thestructures of FIGS. 5A-5B to form the structures of FIGS. 6A-6B, (ii)depositing a second metal oxide layer 133 on first metal oxide layer132, as shown in FIGS. 6A-6B, and (iii) selectively removing theportions of first and second metal oxide layers 132-133 on IO layer 128Nby using a lithographic patterning process on the structures of FIGS.6A-6B to form the structures of FIGS. 7A-7B. Dipole layer 130P inducedbetween first metal oxide layer 132 and IO layer 128N is removed whenthe portions of first and second metal oxide layers 132-133 on IO layer128N are removed. The deposition of first and second metal oxide layers132-133 can include depositing about 0.5 nm to about 3 nm layers ofoxides of metals (e.g., Ga, Al, In, Zn, Nb, Mo, W, or Ta) that haveelectronegativity values greater than the electronegativity values ofmetals or semiconductors (e.g., Hf, Zr, or Ti) in first HK gatedielectric layer 134P. In addition, the layers of oxides (e.g., Ga₂O₃,Al₂O₃, In₂O₃, ZnO, NbO₂, MoO₂, WO₃, or Ta₂O₅) can have an oxygen arealdensity greater than the oxygen areal density of the oxide material(e.g., HfO₂, ZrO₂, or TiO₂) in first HK gate dielectric layer 134P. Insome embodiments, the deposition of first oxide metal layer 132 includesdepositing a layer of transition metal oxide (e.g., ZnO, NbO₂, MoO₂,WO₃, or Ta₂O₅) and the deposition of second metal oxide layer 133includes depositing a layer of oxide (e.g., Ga₂O₃, Al₂O₃, In₂O₃) of ametal from group 13 of the periodic table.

Referring to FIG. 2 , in operation 225, a first HK gate dielectric layerwith a first layer portion on the second metal oxide layer and a secondlayer portion on the IO layer of the NFET is formed. For example, asshown in FIGS. 8A-8B, a first HK gate dielectric layer with a firstlayer portion 134P (also referred to as “first HK gate dielectric layer134P”) on second metal oxide layer 133P and a second layer portion 134N*(also referred to as “first HK gate dielectric layer 134N*”) on IO layer128N is formed. In some embodiments, first HK gate dielectric layers134P-134N* can be formed by depositing about 1 nm to about 2 nm of HfO₂with an atomic layer deposition (ALD) process using hafnium chloride(HfCl₄) as a precursor at a temperature ranging from about 250° C. toabout 350° C.

Referring to FIG. 2 , in operation 230, a doping process is selectivelyperformed on the second layer portion of the first HK gate dielectriclayer. For example, as described with reference to FIGS. 9A-11B, adoping process is selectively performed on first HK gate dielectriclayer 134N*. The selective doping process can include sequentialoperations of (i) depositing a dopant source layer 946 on the structuresof FIGS. 8A-8B to form the structures of FIGS. 9A-9B, (ii) selectivelyremoving the portion of dopant source layer 946 on first HK gatedielectric layer 134P by using a lithographic patterning process on thestructures of FIGS. 9A-9B to form the structures of FIGS. 10A-10B, (iii)performing a drive-in anneal process on the structures of FIGS. 10A-10Bto form doped first HK gate dielectric layer 134N and dipole layer 130N,as shown in FIG. 11B, and (iv) removing dopant source layer 946 from thestructure of FIG. 10B to form the structures of FIGS. 11A-11B.

The drive-in anneal process can implant metal dopants into first HK gatedielectric layer 134N* through diffusion of metal atoms from dopantsource layer 946 into first HK gate dielectric layer 134N*. Theimplanted metal dopants can induce the formation of dipole layer 130N.The drive-in anneal process can include annealing the structures ofFIGS. 10A-10B at a temperature from about 600° C. to about 800° C. andat a pressure from about 1 torr to about 50 torr for a time periodranging from about 0.1 second to about 30 seconds. In some embodiments,the drive-in anneal process can include two anneal processes: (i) a soakanneal process at a temperature from about 600° C. to about 800° C. andat a pressure from about 1 torr to about 50 torr for a time periodranging from about 2 sec to about 60 sec, and (ii) a spike annealprocess at a temperature from about 700° C. to about 800° C. for a timeperiod ranging from about 0.1 second to about 2 seconds.

The deposition of dopant source layer 946 can include depositing a layerof oxide of a rare-earth metal (e.g., La, Y, Sc, Ce, Yb, Er, Dy, or Lu)that has an electronegativity value lower than the electronegativityvalues of metallic or semiconductor materials (e.g., Hf, Zr, or Ti)included in first HK gate dielectric layer 134N. In addition, the layerof oxide (e.g., lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), scandiumoxide (Sc₂O₃), cerium oxide (CeO₂), ytterbium oxide (Yb₂O₃), erbiumoxide (Er₂O₃), dysprosium oxide (Dy₂O₃), or lutetium oxide (Lu₂O₃)) canhave an oxygen areal density smaller than the oxygen areal density ofthe oxide material (e.g., HfO₂, ZrO₂, or TiO₂) included in first HK gatedielectric layer 134N.

Referring to FIG. 2 , in operation 235, a second HK gate dielectriclayer with first and second layer portions on the first and second layerportions of the first HK gate dielectric layer is formed. For example,as shown in FIGS. 12A-12B, a second HK gate dielectric layer with afirst layer portion 136P (also referred to as “second HK gate dielectriclayer 136P”) on first HK gate dielectric layer 134P and a second layerportion 136N (also referred to as “second HK gate dielectric layer136N”) on first HK gate dielectric layer 134N is formed. In someembodiments, second HK gate dielectric layers 136P-136N can be formed bydepositing about 5 nm to about 8 nm of HfO₂ with an atomic layerdeposition (ALD) process using hafnium chloride (HfCl₄) as a precursorat a temperature ranging from about 250° C. to about 350° C. In someembodiments, second HK gate dielectric layers 136P-136N can be depositedthicker than first HK gate dielectric layers 134P-134N.

Referring to FIG. 2 , in operation 240, a pWFM layer is selectivelyformed on the first layer portion of the second HK gate dielectric layerand an nWFM layer is selectively formed on the second layer portion ofthe second HK gate dielectric layer. For example, as shown in FIGS.13A-13B, pWFM layer 124P is selectively formed on second HK gatedielectric layer 136P and nWFM layer 124N is selectively formed onsecond HK gate dielectric layer 136N. The selective formation of pWFM124P and nWFM layers 124N can be performed on the structures of FIGS.12A-12B using lithographic patterning processes to form the structuresof FIGS. 13A-13B.

Referring to FIG. 2 , in operation 245, gate metal fill layers areformed on the pWFM layer and the nWFM layer. For example, as describedwith reference to FIGS. 14A-15B, gate metal fill layers 126P and 126Nare formed on respective pWFM layer 124P and nWFM layer 124N. Theformation of gate metal fill layers 126P-126N can include sequentialoperations of (i) depositing a conductive layer 1426 on the structuresof FIGS. 13A-13B to fill gate openings 412P-412N and form the structuresof FIGS. 14A-14B, and (ii) performing a chemical mechanical polishing(CMP) process on the structures of FIGS. 14A-14B to form the structuresof FIGS. 15A-15B with top surfaces of gate structures 112P-112Nsubstantially coplanar with a top surface of ILD layer 118. In someembodiments, after the CMP process, gate capping layers (not shown) ongate structures 112P-112N and contact structures on gate structures112P-112N and S/D regions 110P-110N can be formed.

FIG. 16 is a flow diagram of an example method 1600 for fabricatingPFET-NFET 102P-102N with cross-sections as shown in FIGS. 1D-1E,according to some embodiments. For illustrative purposes, the operationsillustrated in FIG. 16 will be described with reference to the examplefabrication process for fabricating PFET-NFET 102P-102N as illustratedin FIGS. 17A-26B. FIGS. 17A-26B are cross-sectional views of PFET-NFET102P-102N along lines A-A and B-B of FIG. 1A at various stages offabrication, according to various embodiments. Operations can beperformed in a different order or not performed depending on specificapplications. It should be noted that method 1600 may not producecomplete PFET-NFET 102P-102N. Accordingly, it is understood thatadditional processes can be provided before, during, and after method1600, and that some other processes may only be briefly describedherein. Elements in FIGS. 17A-26B with the same annotations as elementsin FIGS. 1A-1E are described above.

Referring to FIG. 16 , operations 1605-1615 are similar to operations205-215 of FIG. 2 . After operation 1615, structures similar to thestructures of FIGS. 5A-5B are formed. The subsequent formation of layerson IO layers 128P-128N (shown in FIGS. 5A-5B) in operations 1620-1640are described with reference to FIGS. 17A-24B, which are enlarged viewsof regions 103P-103N shown in respective FIGS. 5A-5B.

Referring to FIG. 16 , in operations 1615-1635, gate oxide structuresare formed within the gate openings. For example, as described withreference to FIGS. 17A-23B, gate oxide structures 122P-122N (shown inFIGS. 1D-1E) are formed within respective gate openings 412P-412N (shownin FIGS. 4A-4B).

Referring to FIG. 16 , in operation 1620, a first HK gate dielectriclayer with first and second layer portions on respective IO layers ofthe PFET and NFET 15 formed. For example, as shown in FIGS. 17A-17B, afirst HK gate dielectric layer with a first layer portion 134P* on IOlayer 128P and a second layer portion 134N* on IO layer 128N is formed.In some embodiments, first and second layer portions 134P*-134N* can beformed by depositing about 1 nm to about 2 nm of HfO₂ with an atomiclayer deposition (ALD) process using hafnium chloride (HfCl₄) as aprecursor at a temperature ranging from about 250° C. to about 350° C.

Referring to FIG. 16 , in operation 1625, a doping process isselectively performed on the first layer portion of the first HK gatedielectric layer. For example, as described with reference to FIGS.18A-20B, a doping process is selectively performed on first layerportion 134P*. The selective doping process can include sequentialoperations of (i) depositing a first dopant source layer 1848 on thestructures of FIGS. 17A-17B, as shown in FIGS. 18A-18B, (ii) depositinga second dopant source layer 1850 on first dopant source layer 1848, asshown in FIGS. 18A-18B, (iii) selectively removing the portions of firstand second dopant source layers 1848-1850 on second layer portion 134N*by using a lithographic patterning process on the structures of FIGS.18A-18B to form the structures of FIGS. 19A-19B, (iv) performing adrive-in anneal process on the structures of FIGS. 19A-19B to form dopedfirst HK gate dielectric layer 135P and dipole layer 130P, as shown inFIG. 20A, and (v) removing first and second dopant source layers1848-1850 from the structure of FIG. 19 to form the structures of FIGS.20A-20B.

The drive-in anneal process can implant metal dopants into first layerportion 134P* through diffusion of metal atoms from first and seconddopant source layers 1848-1850 into first layer portion 134P*. Theimplanted metal dopants can induce the formation of dipole layer 130P.The drive-in anneal process can include annealing the structures ofFIGS. 19A-19B at a temperature from about 600° C. to about 800° C. andat a pressure from about 1 torr to about 50 torr for a time periodranging from about 0.1 second to about 30 seconds. In some embodiments,the drive-in anneal process can include two anneal processes: (i) a soakanneal process at a temperature from about 600° C. to about 800° C. fora time period ranging from about 2 sec to about 60 sec and (ii) a spikeanneal process at a temperature from about 700° C. to about 800° C. fora time period ranging from about 0.1 second to about 2 seconds.

FIG. 27 shows the Hf, Zn, Ga, O₂, and Si concentration profiles 138,139, 140, 142, and 144 along line D-D of FIG. 19A before the drive-inanneal process, when first layer portion 134P* includes HfO₂, firstdopant source layer 1848 includes ZnO, second dopant source layer 1850includes Ga₂O₃, and IO layer 128P includes SiO₂, according to someembodiments. FIG. 28 shows the Hf, Zn, Ga, O₂, and Si concentrationprofiles 138, 139, 140, 142, and 144 along line D-D of FIG. 19A afterthe drive-in anneal process. Prior to the drive-in anneal process, thepeak concentrations of Zn and Ga atoms are within the respective regionsof first and second dopant source layers 1848 and 1850, as shown in FIG.27 . Following the drive-in anneal process, the peak concentrations ofZn and Ga atoms shifts to the region of first HK gate dielectric layer135P, as shown in FIG. 28 , thus indicating the implantation of Zn andGa dopants in first HK gate dielectric layer 135P. The peakconcentration of Zn atoms in first HK gate dielectric layer 135P ishigher and closer to interface 135P-128P than the peak concentration ofGa atoms in first HK gate dielectric layer 135P. Such difference betweenthe peak concentrations of Zn and Ga atoms can be achieved by (i) usingfirst dopant source layer 1848 with higher concentration of Zn atomsthan the concentration of Ga atoms in second dopant source layer 1850,and (ii) depositing first dopant source layer 1848 closer to first layer134P* than second dopant source layer 1850 to achieve threshold voltagesbelow about 50 mV (e.g., about 30 mV or 20 mV).

The deposition of first and second dopant source layers 1848-1850 caninclude depositing layers of oxides of metals (e.g., Zn, Nb, Mo, W, Ta,Ga, Al, or In) that have electronegativity values greater than theelectronegativity values of metals or semiconductors (e.g., Hf, Zr, orTi) in first HK gate dielectric layer 135P. In addition, the layers ofoxides (e.g., ZnO, NbO₂, MoO₂, WO₃, or Ta₂O₅, Ga₂O₃, Al₂O₃, or In₂O₃)can have oxygen areal densities greater than the oxygen areal density ofthe oxide material (e.g., HfO₂, ZrO₂, or TiO₂) in first HK gatedielectric layer 135P. The deposition of first and second dopant sourcelayers 1848-1850 can include depositing layers of oxides different fromeach other. In some embodiments, second dopant source layer 1850 may notbe deposited to dope first HK gate dielectric layer with the same metaldopants. In some embodiments, a nitride capping layer (not shown) can bedeposited on second dopant source layer 1850 or on first dopant sourcelayer 1848 in the absence of second dopant source layer 1850 to protectthe underlying layers from thermal degradation during the drive-inanneal process.

Referring to FIG. 16 , in operation 1630, a doping process isselectively performed on the second layer portion of the first HK gatedielectric layer. For example, as described with reference to FIGS.21A-23B, a doping process is selectively performed on second layerportion 134N*. The selective doping process can include sequentialoperations of (i) depositing a dopant source layer 946 on the structuresof FIGS. 20A-20B to form the structures of FIGS. 21A-21B, (ii)selectively removing the portion of dopant source layer 946 on first HKgate dielectric layer 135P by using a lithographic patterning process onthe structures of FIGS. 21A-21B to form the structures of FIGS. 22A-22B,(iii) performing a drive-in anneal process on the structures of FIGS.22A-22B to form doped first HK gate dielectric layer 134N and dipolelayer 130N, as shown in FIG. 23B, and (iv) removing dopant source layer946 from the structure of FIG. 22B. The deposition of dopant sourcelayer 946 and the drive-in anneal process is similar to those describedin operation 230.

Referring to FIG. 16 , in operation 1635, a second HK gate dielectriclayer with first and second layer portions on the doped first and secondlayer portions of the first HK gate dielectric layer is formed. Forexample, as shown in FIGS. 23A-23B, a second HK gate dielectric layerwith a first layer portion 136P (also referred to as “second HK gatedielectric layer 136P”) on first HK gate dielectric layer 135P and asecond layer portion 136N (also referred to as “second HK gatedielectric layer 136N”) on first HK gate dielectric layer 134N isformed. Second HK gate dielectric layers 136P-136N can be formed in anoperation similar to that described in operation 235.

Referring to FIG. 16 , in operation 1640, a pWFM layer is selectivelyformed on the first layer portion of the second HK gate dielectric layerand an nWFM layer is selectively formed on the second layer portion ofthe second HK gate dielectric layer. For example, as shown in FIGS.24A-24B, pWFM layer 124P is selectively formed on second HK gatedielectric layer 136P and nWFM layer 124N is selectively formed onsecond HK gate dielectric layer 136N. The selective formation of pWFM124P and nWFM layers 124N can be performed on the structures of FIGS.23A-23B using lithographic patterning processes to form the structuresof FIGS. 24A-24B.

Referring to FIG. 16 , in operation 1645, gate metal fill layers areformed on the pWFM layer and the nWFM layer. For example, as describedwith reference to FIGS. 25A-26B, gate metal fill layers 126P and 126Nare formed on respective pWFM layer 124P and nWFM layer 124N. Theformation of gate metal fill layers 126P-126N is similar to thatdescribed in operation 245.

The present disclosure provides example multi-Vt devices with FETs(e.g., PFET 102P and NFET 102N) having ultra-low threshold voltages(e.g., about 20 mV to about 100 mV) different from each other andprovides example methods of forming such FETs on the same substrate. Theexample methods form NFETs and PFETs with WFM layers (e.g., pWFM layer124P and nWFM layer 124N) of similar thicknesses, but with ultra-lowand/or different threshold voltages, on the same substrate. Theseexample methods can be more cost-effective (e.g., cost reduced by about20% to about 30%) and time-efficient (e.g., time reduced by about 15% toabout 20%) in manufacturing reliable FET gate structures with lowerand/or different threshold voltages than other methods of forming FETswith similar dimensions and threshold voltages on the same substrate. Inaddition, these example methods can form FET gate structures with muchsmaller dimensions (e.g., thinner gate stacks) than other methods offorming FETs with similar threshold voltages.

In some embodiments, NFETs and PFETs with different gate structureconfigurations (e.g., gate structures 112P-112N), but with similar WFMlayer thicknesses, can be selectively formed on the same substrate toachieve ultra-low and/or different threshold voltages. The differentgate structures can have HK gate dielectric layers (e.g., HK gatedielectric layers 135P and 134N) doped with different metallic dopants.The different metal dopants can induce dipoles of different polaritiesand/or concentrations in dipole layers (e.g., dipole layers 130P-130N)at interfaces between the HK gate dielectric layers and IO layers. Thedipoles of different polarities and/or concentrations result in gatestructures with different EWF values and threshold voltages. In someembodiments, HK gate dielectric layers can be doped with dopants of twodifferent materials to induce dipoles of different materials thatprovide stronger electric fields and lower threshold voltages. Thus,controlling the dopant materials and/or concentrations in the HK gatedielectric layers can tune the EWF values of the NFET and PFET gatestructures, and as a result can adjust the threshold voltages of theNFETs and PFETs without varying the WFM layer thicknesses. In someembodiments, instead of the doped HK gate dielectric layer, PFET gatestructure can include dual metal oxide layers (e.g., first and secondmetal oxide layers 132P-133P) interposed between the HK gate dielectricand the IO layer to induce dipoles of different materials between the HKgate dielectric layer and the IO layer.

In some embodiments, a method includes forming a fin structure on asubstrate, forming a gate opening on the fin structure, forming aninterfacial oxide layer on the fin structure, forming a first dielectriclayer over the interfacial oxide layer, forming a dipole layer betweenthe interfacial oxide layer and the first dielectric layer, forming asecond dielectric layer on the first dielectric layer, forming a workfunction metal (WFM) layer on the second dielectric layer, and forming agate metal fill layer on the WFM layer. The dipole layer includes ionsof first and second metals that are different from each other. The firstand second metals have electronegativity values greater than anelectronegativity value of a metal or a semiconductor of the firstdielectric layer.

In some embodiments, a method includes forming first and second finstructures on a substrate, forming first and second gate openings on thefirst and second fin structures, respectively, forming a firstdielectric layer with first and second layer portions formed within thefirst and second gate openings, respectively, selectively doping thefirst layer portion with first and second dopants that are differentfrom each other, selectively doping the second layer portion with thirddopants different from the first and second dopants, forming a seconddielectric layer with first and second layer portions on the first andsecond layer portions of the first dielectric layer, and forming firstand second gate metal fill layers over the first and second layerportions of the second dielectric layer, respectively. The first andsecond dopants have electronegativity values greater than anelectronegativity value of a metal or a semiconductor of the firstdielectric layer. The third dopants have an electronegativity value lessthan an electronegativity value of the metal or the semiconductor of thefirst dielectric layer.

In some embodiments, a semiconductor device includes a substrate, a finstructure disposed on the substrate, a semiconductor oxide layerdisposed on the fin structure, a first metal oxide layer disposed on thesemiconductor oxide layer, a second metal oxide layer disposed on thefirst metal oxide layer, a first dielectric layer disposed on the secondmetal oxide layer, a second dielectric layer disposed on the firstdielectric layer, a work function metal (WFM) layer disposed on thesecond dielectric layer, and a gate metal fill layer on the WFM layer.The second metal oxide layer is different from the first metal oxidelayer. Metals of the first and second metal oxide layers haveelectronegativity values greater than an electronegativity value of ametal or a semiconductor the first dielectric layer.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method, comprising: forming a fin structure ona substrate; forming a gate opening on the fin structure; forming aninterfacial oxide layer on the fin structure; forming a first dielectriclayer over the interfacial oxide layer; forming a dipole layer betweenthe interfacial oxide layer and the first dielectric layer, wherein thedipole layer comprises ions of first and second metals that aredifferent from each other, and wherein the first and second metals haveelectronegativity values greater than an electronegativity value of ametal or a semiconductor of the first dielectric layer; forming a seconddielectric layer on the first dielectric layer; forming a work functionmetal (WFM) layer on the second dielectric layer; and forming a gatemetal fill layer on the WFM layer.
 2. The method of claim 1, wherein theforming the dipole layer comprises: forming a first metal oxide layer onthe interfacial oxide layer; and forming a second metal oxide layer onthe first metal oxide layer, wherein the second metal oxide layer isdifferent from the first metal oxide layer.
 3. The method of claim 2,wherein the forming the first or second metal oxide layer comprisesdepositing an oxide of a metal that is different from a metal of thesecond dielectric layer.
 4. The method of claim 2, wherein the formingthe first or second metal oxide layer comprises depositing an oxide ofzinc, niobium, molybdenum, tungsten, tantalum, gallium, aluminum, orindium.
 5. The method of claim 2, wherein the forming the first metaloxide layer comprises depositing an oxide of zinc, niobium, molybdenum,tungsten, or tantalum, and wherein the forming the second metal oxidelayer comprises depositing an oxide of gallium, aluminum, or indium. 6.The method of claim 1, wherein the forming the dipole layer comprisesdepositing first and second metal oxide layers on the interfacial oxidelayer, and wherein the first and second metal oxide layers have oxygenareal densities greater than an oxygen areal density of the firstdielectric layer.
 7. The method of claim 1, wherein the forming thedipole layer comprises forming first and second dipoles with first andsecond concentrations that are different from each other.
 8. The methodof claim 1, wherein the forming the dipole layer comprises: depositing afirst layer of metal oxide with a first thickness, depositing a secondlayer of metal oxide with a second thickness that is less than the firstthickness, and wherein the first and second layers of metal oxides havemetals different from each other.
 9. A method, comprising: forming firstand second fin structures on a substrate; forming first and second gateopenings on the first and second fin structures, respectively; forming afirst dielectric layer with first and second layer portions formedwithin the first and second gate openings, respectively; selectivelydoping the first layer portion with first and second dopants that aredifferent from each other, wherein the first and second dopants haveelectronegativity values greater than an electronegativity value of ametal or a semiconductor of the first dielectric layer; selectivelydoping the second layer portion with third dopants different from thefirst and second dopants, wherein the third dopants have anelectronegativity value less than an electronegativity value of themetal or the semiconductor of the first dielectric layer; forming asecond dielectric layer with first and second layer portions on thefirst and second layer portions of the first dielectric layer; andforming first and second gate metal fill layers over the first andsecond layer portions of the second dielectric layer, respectively. 10.The method of claim 9, wherein the selectively doping the first layerportion with the first and second dopants comprises: forming first andsecond dopant source layers on the first and second layer portions ofthe first dielectric layer; removing portions of the first and seconddopant source layers on the second layer portion of the first dielectriclayer; and performing an annealing process.
 11. The method of claim 10,wherein the forming the first or second dopant source layer comprisesdepositing an oxide material with an oxygen areal density greater thanan oxygen areal density of an oxide material of the first dielectriclayer.
 12. The method of claim 10, wherein the forming the first orsecond dopant source layer comprises depositing an oxide of zinc,niobium, molybdenum, tungsten, tantalum, gallium, aluminum, or indium.13. The method of claim 10, wherein the forming the first dopant sourcelayer comprises depositing an oxide of zinc, niobium, molybdenum,tungsten, or tantalum, and wherein the forming the second dopant sourcelayer comprises depositing an oxide of gallium, aluminum, or indium. 14.The method of claim 10, wherein the forming the first dopant sourcelayer comprises depositing a first layer of metal oxide with a firstthickness, wherein the forming the second dopant source layer comprisesdepositing a second layer of metal oxide with a second thickness that isless than the first thickness, and wherein the first and second layersof metal oxides have metals different from each other.
 15. The method ofclaim 9, wherein the selectively doping the second layer portion withthe third dopants comprises: forming a rare-earth metal oxide layer onthe first and second layer portions of the first dielectric layer;removing a portion of the rare-earth metal oxide layer on the firstlayer portion of the first dielectric layer; and performing an annealingprocess.
 16. The method of claim 15, wherein the forming the rare-earthmetal oxide layer comprises depositing an oxide material with an oxygenareal density less than an oxygen areal density of an oxide material ofthe first dielectric layer.
 17. A semiconductor device, comprising: asubstrate; a fin structure disposed on the substrate; a semiconductoroxide layer disposed on the fin structure; a first metal oxide layerdisposed on the semiconductor oxide layer; a second metal oxide layerdisposed on the first metal oxide layer, wherein the second metal oxidelayer is different from the first metal oxide layer; a first dielectriclayer disposed on the second metal oxide layer, wherein metals of thefirst and second metal oxide layers have electronegativity valuesgreater than an electronegativity value of a metal or a semiconductor ofthe first dielectric layer; a second dielectric layer disposed on thefirst dielectric layer; a work function metal (WFM) layer disposed onthe second dielectric layer; and a gate metal fill layer on the WFMlayer.
 18. The semiconductor device of claim 17, further comprising adipole layer disposed at an interface between the first metal oxidelayer and the semiconductor oxide layer.
 19. The semiconductor device ofclaim 18, wherein the dipole layer comprises metal atoms of the firstand second metal oxide layers and oxygen atoms of the semiconductoroxide layer.
 20. The semiconductor device of claim 17, wherein oxygenareal densities of the first and second metal oxide layers are greaterthan an oxygen areal density of the first dielectric layer.